US2615135A - Mass analyzing apparatus - Google Patents

Description

Oct. 21, 1952 w. a. GLENIN, JR 2,615,135

MASS ANALYZING APPARATUS Filed June 20, 1950 3 0- GA L VANOMETER F/LAMENT POWER SUPPLY 0 l/AR/ABLE REG 7 GENERATOR DIRECT CURRENT POWER SUPPLY VACUUM PUMP INVENTOR. W/LL/AM E. ELENA/,Jn

Patented Oct. 21, 1952 MASS ANALYZING APPARATUS .e

Wi1liam-E;-- Glenn; J r'.,' Berkeley, Calif'.;' assignor.

t' -the-- Uiiit'ed States of America :as represented l by the zUnitedistates Atomic: Energy commis-s- SiOll-Ii The present invention relates generally --tothe segregation and identification of component elements and compounds -in a mixture of unknown quality and more particularly relates to quantitative and qualitative mass analysis-of ionizablemixtures.

Present day reSearc-hdn the fields-of physics and-chemistry, as well asmany other theoretical and-industrial fields} has emphasized the need" Figure :1 is a longitudinal cross sectionview of oneuembodiment'of theinvention with associated electrical connections shown-in block form, and

Fig. 2 is an isometric projection of-the same embodiment shown'in'Fi'g. 1 withthecover removed to show the-physical relation of the elements thereof. I

Considering the physical characteristics and elements 1 of theembodiment of theinvention for AadQQII-atG 'aHQJyZiIIg techniques adapted' to shownin Figs; -1 'and-2, it will be noted that the rapidly identify component elementsand'com apparatus-isenclo'sedby an envelopel having-a pounds'--comprising-unknown-mixtures In the pipe -2 leading-therefrom to a vacuum pump or. effort' toe fulfillthis need-"numerous types of system (not -shown) whereby the interior ofmethods and apparatus have- -been developed, theenvelope may be evacuated to the proper opamong which-mass-spectrometry has pr0ven one erating pressurer Envelope fl maytake the "form of the-more satisfactory. Rather rapid and acoi-a-box orcylinder open'at one-end-andpref-' curate analysis may be-accomplishedby electro erably" having aflange 4 about the open end magnetic" separation; however the-- magnetic thereof; therebyfacilitating the fastening therefield of necessity associated'witli the-apparatus to -0f-envelope closuremeans such'as face plate presents certain difficulties. In order to establish 3 which may-be secured by means of bolts or the required-magnetic fieldit-is necessary to -proscrews 6 passing through face plate 3 and engag- Vide -ratherlarge and-cumbersome-equipment ing fiange ljas shown-in-Fig. 1. The joint be- Whi-c-h fo'r-many applicationsis disadvantageous tween envelope' l and fa'ce platei is maintained not only because-ofspace and 'weightrequirevacuumtight by anannular gasket fitting into ments but also becauseof the-high cost of concorresponding-grooves in face plate 3 and flange 4. strfuctiont Thus despite the success ofmass Within enveloped there is centrally-situated spectrometry in the-field of analysis it still reanelectrode arrangement consistingof a pair of mains-fora simple-accurate, rapid acting, and fiat parallelmetallic plates 8 and-Al extendinginexpensive -apparatus to be -developed which substantially perpendicular to-face platet into will fu'lfill the-need-therefor. venvelope l and' electrically and mechanically- Accordinglyyit'is an'object' of'the present injoined together by-a metallic end piece -ll which vention- -to provide an' improved *method' and mayei-therlee-integrally formed with plates 8 and means for the rapidand accurate analysis of 9'--"0rsecured thereto by suitable means.- Endth components of a mixture in accordance with plate -ll abuts face plate 3 and is rigidly securedtlietindividual massnumbers thereof ;thereto, as for example, by machinescrews-H Another object of-the present invention is to p ughend plate -l| and-threaded into provide an :improvedmethodand means of elecface plate-3. Midway between electrode platestro-statical-ly accomplishing mass analysis. B and-'9 and parallelthereto, there is situated "a Still-another-object of-the present invention d-'0 r d 3" f-appr x is to provide a very compact meansfor analyzing 40- y' -le h and W dth as 1 1M658 th n tituentamasses'of a mixture. and 9,- and formed--'of a metallic mesh onscreenn t ct "of-the t invention i X of'a suitable size toallow-'passage therethrough to provide -an improved means for acting upon of 1 electrified particles: Intermediate electrode" ions wi-tha combination of directand-alternatin l3 is'secured at one end to a leadin insula'tor electrical fields to. identify =ions-=of different 4514,- such as-aKoVar-glass seal, having a n. masses}; tra-lly located conductor therethrough'; which, A 'still furtherobject 'ofthe-present invention in-turnextends-through both face plate? 3 and; is-toprovideanimprovedmethodand means endplate' I l in fixed vacuum" tight. relation: for-*producin'g controlled oscillation of an ion thereto, thereby-supporting "intermediate" ele'c beam-to separate and identify the ions of differ- '50 Itrode-l3 and providing an electrical connection ent masses' therein. thereto exterior to envelope I At the 'other end Many other possible-objectsyadvantages; and" 0f intermediate-electrode13" thereis provided a; uses of the invention will become apparent from pair of insulators- I 6 of equal length separating. the following disclosure taken toget-herwiththeintermediateelectrode I3 from" platesra "and "9 appended drawings wherein? Jandproviding insulation betweenintermediate electrode I3 and plates 8 and 9 as well as mechanical rigidity and support of one terminus of the electrode assembly by virtue of screws I'I engaging insulators I5 and urging intermediate electrode I3 and plates 8 and 9 into intimate bearing relationship with opposite ends of insulators I6.-

Before proceeding with the description it should be noted that the above-described electrode assembly consists of a pair of plate electrodes parallel to and equidistant from an intermediate wire mesh electrode, all being secured together in a rigid assembly with the plate electrodes being electrically connected to the surrounding envelope and the intermediate electrode being electrically connected to an external terminal.

Also within envelope I, there is provided an ion source or filament I8 and an ion collector I9, each of which may advantageously consist of a metal strip oriented with its major dimension perpendicular to the major dimension of the plate electrodes 8 and 9; however, other suitable types of sources and collectors, as well as relative orientation thereof, may be employed. In the illustrated embodiment of the invention the filament I8 and the collector I9 are disposed parallel to and adjacent opposite ends of plate electrode 8 and in close proximity to the intermediate electrode presented face of plate 8. In order to provide for easy removal of filament source I8 and collector I9 a pair of apertures 29 and 2I are formed in plate electrode 8 directly above filament I8 and collector I9 and of slightly larger size than these elements. Filament I8 is supported in position by a pair of rigid filament wires 22 secured to opposite edges thereof and secured to a pair of insulators 23 extending through face plate 3 in fixed relation thereto. In the illustrated embodiment of the invention insulators 23 are of the type having a central conducting portion connecting external terminals to filament wires 22 internal to envelope I and having an external metal collar which may be joined as by soldering to face plate 3 about the aperture therein through which the insulator extends to form a vacuum tight seal; however, it Will be appreciated that numerous types of filament supporting and energizing means may be employed, as well as various types of insulators and vacuum seals in connection therewith. For many applications of the invention it is advantageous to provide a readily removable filament which may of course be accomplished by conventional mechanical apparatus, all within th scope of the invention.

Collector I9 may be conveniently mounted by means of an inverted cup shaped bracket 24 disposed above the center of aperture 2| and secured to the top surface of plate electrode 8. An insulator 26 of the type having a central conductor therethrough, extending through the top of bracket 24, is rigidly secured to collector I9 whereby collector I9 is supported in position. The length of insulator 26, or of some intermediate connecting link, such as rigid wire, is chosen so that collector I9 is disposed a short distance below the lower face of plate 8. equal to the spacing of filament I8 from plate 8 for reasons set forth below in the description of operation of the invention. Connected to the top of the conductor extending through insulator 26 is a collector lead 21 extending therefrom toward face plate 3, in the vicinity of which lead 21 electrically contacts the central conductor of an insulator 28 of the same or similar type as described above, which extends through face plate 3 in vacuum tight relation thereto and presents a terminal external to envelope I which is electrically connected to collector I9.

It will thus be noted that internal to envelope I there is provided, in addition to the previously described electrode assembly, a filament and a collector disposed intermediate plate electrodes 8 and 9 and in close proximity with plate 8 at opposite ends thereof, with associated electrical leads extending outside of envelope I in insulated relation thereto and providing connections for energization of filament I8 and measurement of the current at collector I9.

Considering an electrical system adapted for use with the above-described elements and referring to Fig. 1 for illustration thereof, it will be noted that a direct current power supply 3I is connected between envelope I and the central conductor of insulator I4 which leads to intermediate electrode I3; envelope I being connected to the positive side of power supply 3| and to I electrodes 8 and 9. In addition to the direct current voltage applied between electrodes 8 and 9 and intermediate electrode I3, there is applied an alternating voltage therebetween by means of an alternating current power supply 32 connected across D. C. power suppl 3|. A. C. power supply 32 may conveniently comprise a variable frequency radio-frequency voltage generator for the mode of operation contemplated by the illustrated embodiment, as will be clarified in the following description of operation, and thus to preclude ambiguity the A. C. power supply will hereinafter be referred to as R. F. generator 32.

Heating current for filament I8 is provided by a filament power supply 33 which is connected between filament leads 22 through lead-in-insulators 23 and is connected to the positive lead of D. C. power supply 3 I. One further element completes the electrical circuit of the device, and that is a current measuring device such as a galvanometer 34 which is connected between envelope I and collector I9 through lead-in-insulator 28.

Now that the physical construction of the invention and the electrical elements and circuits associated therewith have been fully disclosed the operation of the invention may be considered. Prior to actual analysis, a sample to be analyzed is placed on the lower face of filament I8 and the envelope I is evacuated to a relatively high vacuum. It will be appreciated that the analysis of minute sample will be facilitated by forming a liquid solution or suspension thereof and painting same upon filament I8. The plate electrodes 8 and 9 and the intermediate electrode I3 are biased from D. C. power supply III and R. F. generator 32, which establishes an electrostatic field between plate electrodes 8 and 9 and intermediate electrode I 3, for convenience the electric field resulting from the D. C. potential being considered as directed away from intermediate electrode I3. An electric field is also established between end plate II and intermediate electrode I3 by virtue of the fact that end plate I I electrically contacts plate electrodes 8 and 9 and while the electric field between plate electrodes 8 and 9 and intermediate electrode I 3 is substantially perpendicular to the faces thereof, it should be noted that end plate II is disposed perpendicularly to intermediate electrode I3 and thus the electric field therebetween is generally skew or bowed with a component parallel to the faces of the plate and intermediate electrodes. Following introduction of the sample in the apparatus, evacuation of the envelope and..bias+. ing of the electrodes, allas noted abovefilament I8 is heated by an electric current fiowingdirectly therethrough from filament power supply;33 vial. filament leads 22. Heating of filament I8 ionizes. the sample previously placed thereon: and. ions. of

the constituent elements or. compounds ofthe sample are formed. The ions formed at. filament: I8 areattracted therefrom by the negative potentialupon intermediate electrode I3 and these ions are .thus. accelerated toward electrode I3; how ever,..insteadq of. impinging .upon'. intermediate.

electrode I3 the ions pass directly. through same.-

because of. the open construction thereof; After. passingthrough intermediate. electrode-.13.. the

ions :enter .a decelerating electric field resulting from; the positive 1D. 0. potential. on. plate .elec-a.

trode .9;and .the negativeD. .C- field .impressed upon intermediate electrode. I3, the result being that theions reverse direction in the vicinity of 1: plate. electrode :9 and are;accelera-ted toward in;-.

termediate electrode '13.; The ions again; pass through intermediate .electrode I3 andare again subjected to a deceleratingelectric field produced by the relatively positive .potentialupon .plate electrode 8 which causes another reversalof the. direction of motion of .the ions- It is thus. ap- I parent that,.considering only the D. C..potentials:

ate electrode I3 is bowed or skew with respect to. the surface of intermediate electrode I3 and thus:

may be considered as having a componentv along theielectrodes toward collector I9; This component of the electric field acceleratesions leave ingfilament. I8 in adirection away from end plate IIand becauseof the lack of anydecelerating.

influence, the ions travel along the plate and intermediate electrodestoward collector I9 while oscillatingunder the influence of the DC. electric field.

From the above considerations, it 1 isevide'nt that collection of ions produced at filament I8 may be I accomplished by proper disposition of collector element I9, or.:more practically by a proper; choice of the relative values. of thefield producing oscillation andthe fieldproducing ion migration along the electrodes. Adjustment of the direction and thus the horizontal component ofthe D. C. electric field in the vicinity of end plate II may be accomplished by varying the configuration of end plate II or by the employment of metallic plates of appropriate disposition and configuration to deform the electric field and.

thereby determine its horizontalcomponent. By thesemeans the number of oscillations which the-ions undergo prior to reaching the collector is controlled and alsothe disposition of the oscillation nodes is determined whereby collection at collector I9 is accomplished.

Itwill be noted that the displacement of filamentzIR from intermediate electrode I3-is equal. to. the displacement of collector I9 from-inter-i mediate electrode I3. As the magnitude of the ion .oscillations remains unchanged as the ions travel: along the electrodes toward collector I 9 thetions will impinge upon collector =I9 thereby mined masscorrespondingto a knownconstitue;

ent ;0fthe sample..material ionized, a radio-freequency .;voltage from; .R: generator; 32 :is 1 .emas ployed... The. impression .ofv ar.radio-fr'equencyz. voltage upon-intermediate electrode. I3 causes: an 1 alternating .electriclfield. to be superimposed :uponsr: the..D..' C. .field discussed. above... It may'xbe easily; shown thatpositive .ions. which. are. in: phase with'.. the t: radioef-r'equency variations in; theelectric .1 fieldr-andwstay .in. :phase. through; a; whole ecycle thereof. will .sufier. .no net. change .in rtheir: V6100: itiesi Thusions whichdeave filament; I8 rwhenz. intermediate electrode. I 3 :1 has zero radios-fre quency' voltagethereon, .pass through intermediate electrode: I 3 .when. it has. a maximum positive J,

radioefrequency voltage thereon,:.reach;the:.clos= A estupointinv their traverseto .plateselectrodelfl 1; when; the. radio=frequency voltage oninter-medie atet electrode: I 3 .t is :lzero,. returnthrough. inter,-

mediate electrode: I3.-when theiradio-frequencyo ions it will be noted that suchsionsare subjected to an:.increasedv acceleration: toward. zand..a.away from plate. electrode. 9 :with.respe.ct;:: to inter?" mediate. electrode. I3 sand .a 1decreased...accelerae..- tiontowardandxaway fromplate/S :whichthereby produces ,a netuequal acceleration.towardLamL away .from. either :plate. electr0de..-with, respect. to. the otherplate electrode: It :will .be ;;further.::- notedthat; ions which are out. of: phase *with the.v radio-.frequency. voltagewill have anet; accelera tionincrease, or, decrease iduringacycleand that. these. ions,.;will progressively fall further-;out of phase .until. they receive a 1 suflicient;increase-= in. acceleration that; they: impinge one. ;of the platelelectrodesr g V The..,.ve1oc i.ty of. :ions within the lapparatus is dependent uponthe .chargeeto-mass ratio of: the ionsand the. strength of the electric field-to ,which they are subjected and, as the same, electric field; influences all ions leaving filament I 8 atrany particular. instant, the relative velocityof the ionsis proportional only to their relative chargetoemass .ratios.: For the purpose of this discussion allions may be assumed to have the same charge .and thus the. ion velocity is dependent. only upon the mass thereof. In order for ions to remain in phase with the radio-frequency ,voltagethe ions must make, onejcomplete ,oScil1ation inv one. cycle of voltage. and, as the velocity, of theions is dependentnupon their mass, only, ions of one particularv mass will stay inv phase with the radioefrequency voltage of any .par: ticular frequency. Ions of. any mass other;.than: the one which acquiresthe proper average veloc-. ity .to-stay in phase with .theradio-frequency voltage. become progressively further and further out of phaseat each cycleand eventually receive sufficient acceleration during. one-half. cycle to impinge upon one of plate electrodes .8 or- S!.- Thus only ions of a particular mass cor..-.-- responding .to one particular frequency. 'of. ..the

radio-frequency voltage are collected at collector I9 and as this frequency is inversely proportional to the square root of the mass it is possible to accurately identify the mass of the particular ion impinging the collector I9 at any predetermined frequency of the radio-frequency voltage. In practice it has been found advantageous to calibrate the R. F. generator 32 directly. in

mass units so that the frequency may be adjusted to any particular settingcorresponding to a. specific mass and no calculations are necessary to identify the ions collected. With the R. F. generator variable frequency control calibrated directly in mass units it is only necessary to'successively position the control on the various masses and note the galvanometer reading for each in order to analyze the sample and identify the ions formed therefrom.

Mass analysis, or identification of the constituents of a sample of unknown quality is made simple and rapid by the present invention. In addition, the size, complexity, and cost of the equipment. required for mass analysis is materially reduced by the present invention. Many other advantages, as well as variations in the structural details and mode of operation, all within the scope of the invention, will suggest themselves to those skilled in the art from a study of the present disclosure and although the invention has been disclosed with respect to only one preferred embodiment it is not intended to solimit the invention; attention being directed to the following claims for a precise delineation of the scope of the invention.

What is claimed is:

'1. Analyzing apparatus comprising a pair of parallel spaced electrodes, means establishing a constant electric field directed perpendicularly to said electrodes from a position equidistant therebetween, means for ionizing a sample to be analyzed and subjecting said ions to the effects of said electric field whereby said ions oscillate between said electrodes, means for imparting a velocity to'said ions parallel to said electrodes whereby said ions travel between said electrodes, means for varying the amplitude of said electric field at a known frequency whereby only ions of a mass inversely proportional to the square of the frequency continue oscillatory travel between said electrodes without impinging thereon, and means to collect the ions having a mass proportional to said frequency and to indicate the current produced thereby.

2. Mass analyzing apparatus comprising a pair of parallel spaced electrodes having a positive potential impressed thereon, a perforated electrode disposed intermediate and parallel to said pair of electrodes and at a negative potential with respect thereto whereby an electric field is established perpendicular to said electrodes, means supplying ions of a sample to be tested adjacent the perforated electrode presented face of one of said pair of electrodes whereby said ions are accelerated and constrained to oscillate between said pair of electrodes through said perforated electrode, ion collection means disposed adjacent the perforatedelectrode presented face of one of said pair of electrodes and separated therefrom by substantially the same distance as separates the ion supply means from the electrode adjacent thereto, means urging said ions toward said ion collection means from said ion supply means, and means varying the potential difference between said perforated electrode and said, pair of elec-v trodes at a known frequency whereby only ions 8 of a particular known mass are unaffected thereby and impinge said collector.

.3. Mass analyzing apparatus comprising means establishing a region defining a pair of constant electrostatic fields having a common negative boundary, an ion source for ionizing a sample to be analyzed and injecting the ions into said elec trostatic field region whereby positive ions of said sample oscillate within said region under the influence of said electrostatic fields, means for varying the magnitude of said electrostatic fields in a predetermined cyclic manner whereby ions of apredetermined mass have a constant magnitude of oscillation, and means for collecting the ions having a constant magnitude of oscillation.

4. Mass analyzing apparatus comprising means establishing a region defining a pair of contiguous opposed electrostatic fields, ion source means providing ions of a sample to be analyzed within said region adjacent the boundary thereof whereby said ions oscillate under the influence of said electrostatic fields, means for imparting a velocity to said ions in a direction normal to said electrostatic fields, means for cyclically varying the strength of said electrostatic fields at a known frequency whereby only ions of one predetermined mass retain constant amplitudes of oscillation, means for collecting the ions having constant amplitudes of oscillation, and means for changing the frequency of said cyclic variation in electrostatic field strength to collect ions of other predetermined masses.

5. Mass analyzing apparatus comprising ion source means for ionizing a sample to be analyzed, first electrostatic field producing means for accelerating ions from said ion source in a predetermined general direction with a velocity proportional to the relative masses thereof, collection means disposed at a distance from said ion source in the general direction of travel of said ions, second electrostatic field producing means operating at a predetermined frequency to accelerate ions of all but one mass which is inversely proportional to the square of saidoperating frequency, and means for stopping said accelerated ions short of said collector whereby only ions of one mass impinge said collector.

6. A mass analyzer apparatus as set forth in claim 5 further characterized by frequency control means connected to said second electrostatic field producing means for varying the frequency of operation thereof whereby ions of masses corresponding to different frequencies impinge said collector, and indicating means connected to said collector means for indicating the collection and relative amount of ions of different masses impinging thereon.

7. Mass analyzing apparatus comprising an evacuated envelope, a pair of parallel spaced plates disposed within said envelope, a mesh electrode disposed intermediate and parallel to said plates and equidistant from each other, power supply means impressing a negative direct current potential upon said electrode relative to said plates, means establishing an electrostatic field parallel to said plates and electrode, ion source means interior to said envelope and introducing ions of a substance to be analyzed into the region between said plates and said electrode whereby said ions oscillate between said plates through said mesh electrode and travel along said plates under the influence of said electrostatic field, ion collection means disposed in the region between said plates and said electrode, and a power supply providing alternating current voltage and connected between said plates and said electrode whereby ions out of phase therewith experience increased amplitudes of oscillation and only ions of a predetermined mass maintain constant oscillation amplitude and reach said collector.

8. A mass analyzer comprising an evacuated envelope, a pair of spaced parallel plates Within said envelope, a mesh electrode disposed equidistant from each of said electrodes intermediate thereto and parallel to said electrodes, an ion source and an ion collector each disposed adja- --cent one of said plates intermediate the plate and said mesh electrode, said source and collector being separated along said plate, electrostatic field producing means adjacent said ion source and urging ions from said source toward said ion collector, and power supply means connected between said plates and said mesh electrode and impressing a direct current potential therebetween whereby said mesh electrode is maintained at a negative potential relative to said plates and an alternating current potential therebetween whereby the amount by which said mesh electrode is negative with respect to said plates is varied and thereby constraining ions from said ion source traveling toward said collector to oscillate between said plates through said mesh electrode with ions of a predetermined mass being in phase with said alternating current potential and impinging upon said collector.

9. A mass analyzer comprising an evacuated envelope, a pair of spaced parallel plates disposed within said envelope, a first electrode electrically connecting said plates at one end thereof, a second electrode having an open mesh structure disposed intermediate said plates, said second electrode being equidistant from said plates and insulated therefrom, first power supply means connected between said second electrode and said plates and impressing a direct current potential therebetween with said second electrode being maintained at a negative potential relative to said plates and first electrode, second power supply means connected between said plates and second electrode and impressing therebetween an alternating current potential of a lesser magnitude than said direct current potential, an ion source adjacent one of said plates and intermediate said plate and second electrode, said source being also adjacent said first electrode and being electrically connected to said plate, an ion collector disposed adjacent the same plate as said ion source and separated from said source in a direction away from said first electrode, an indicating means connected to said collector and indicating the ion current of ions of a predetermined mass passing through the analyzer in phase with said alternating current potential.

10. A mass analyzer as claimed in claim 9 further defined by said second power supply means having a controlled variable frequency output potential whereby ions of different predetermined masses are in phase with said alternating current potential applied between said plates and second electrode and are collected at said ion coljector and the relative amount thereof indicated by said indicating means.

WILLIAM E. GLENN, J 3.

REFERENCES CITED UNITED STATES PATENTS Name Date Langmuir Mar. 6, 1945 Number

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